Typically, the curing and drying of tobacco involves four phases. First, the tobacco is subjected to a coloring or yellowing process. Secondly, the leaf is wilted. Thirdly, the curing and drying process involves leaf drying. Finally, the curing and drying process includes stem drying. It is known to utilize ethylene during the first or yellowing phase of the curing and drying process. For example, see my earlier U.S. Pat. No. 4,836,222.
In the past, ethylene has been produced by the farmer in what has referred to as a catalytic generator. While the ethylene produced is not pure, farmers have used the product ethylene in the very beginning stages of yellowing. Besides the catalytic generator, farmers have used pure or even near pure ethylene from cylinders in the tobacco curing and drying process. In the case of both ethylene produced from a catalytic generator or dispensed from a cylinder, the farmer has typically simply treated the tobacco within the curing and drying structure with ethylene prior to subjecting the tobacco to the effective coloring temperatures. Generally, in this process at the beginning of the curing and drying schedule, ethylene is dispensed within the barn and the ethylene mixes with a system of circulating air and the tobacco is exposed to the ethylene-air mixture as the system of air is circulated through the barn. Typically, the temperature within the barn during the application of ethylene is maintained at or near ambient conditions. Presently, it is the recommended practice to condition or treat the tobacco with ethylene while the temperature within the barn or the drying structure is maintained at ambient temperature conditions, approximately 70.degree.-85.degree. F. In most cases, this has meant that no heat is added during the ethylene application phase of the curing and drying schedule. However, farmers have added heat during ethylene applications where the outside ambient temperature was sufficiently cool that heat was required to maintain a temperature range of 70.degree.-85.degree. in the barn.
Prior practices in curing and drying tobacco with ethylene has called for a two-step approach. The tobacco is first subjected to being conditioned by an ethylene-air mixture at ambient temperature for a selected time period. Once this conditioning step has concluded, the application of ethylene is discontinued and the second step of coloring or yellowing then proceeds. This second step entails raising the temperature from ambient conditions to the effective coloring or yellowing temperature range which is typically 90.degree.-105.degree. F. For the past several years this has been the standard curing and crying practice within the flue cured tobacco regions of the United States where farmers have utilized ethylene.
As pointed out above, ethylene has been used to facilitate the yellowing of tobacco in the curing and drying process. As also pointed out above, it has been a standard practice for the ethylene to be applied to the tobacco at ambient temperatures, approximately 75.degree.-90.degree. F. The reasons for this accepted practice is not totally clear but apparently farmers, ethylene suppliers, and some individuals knowledgeable in curing and drying tobacco have concluded that ethylene is most effective at ambient temperature conditions, that is temperatures of approximately 70.degree.-90.degree. F. One cannot be totally sure why this has been the practice. It is speculated that the fact that vegetables and fruits have been subjected to ethylene under purely ambient temperature conditions may have been an underlying factor that gave rise to this particular practice. Tobacco curing and drying is quiet different from simply ripening vegetables and fruits in as much as one must view the curing and drying process as a total process where not only the leaf is yellowed but the total leaf including the stem is subjected to an extensive drying process.
Therefore, while applying ethylene to tobacco during the curing and drying process has in the past offered advantages to the farmer, the curing and drying process with ethylene has not significantly reduced the total curing and drying time for tobacco as compared to conventional practices without ethylene.
Tobacco farmers have longed looked for ways to shorten the time period required to completely cure and dry tobacco. The reason for this is basically one of the economics. If the tobacco farmer is able to shorten the time period for curing and drying, that translates into a need for fewer tobacco barns for a given crop size and that means less capital outlay for such barns or curing and drying structures. Beyond that, it is also possible to save fuel and electricity costs by decreasing the total curing and drying period.
Therefore, there has been a need and a desire to decrease the time period required to cure and dry tobacco. While there is some evidence that the use of ethylene in a tobacco curing and drying process has the potential to shorten the curing and drying period, results do not clearly indicate a consistent and substantial decrease in curing and drying time.